Intercellular communication is essential for homeostatic function of most organs, to coordinate events during development, and to pace contractions in the heart, lungs, gut, erectile tissue and uterus. Published reports from the principal investigator's group now indicate that coordination of cellular activities through gap junctions is vital in flexor tendons in response to mechanical load and wounding. Exercise is critical to health maintenance: normal activity is positive, immobilization is negative and overactivity is destructive. In medicine, motion therapy post-injury is essential to recover range of motion. The applicants hypothesize that coordination of cellular activities through gap junctions is vital in response to mechanical load and after tendon injury. If gap junctions are blocked, cell coordination will be prevented. In Specific Aim 1, they will test the importance of gap junctions in signaling via Ca2+, gap junction translocation with a GFP-cx43 construct, and DNA and collagen synthesis in cells that have been mechanically loaded and wounded in vitro +/- gap junction blockage. Loading will include both acute and adaptive regimens. In Specific Aim 2, they will test the effect of PKC modulation on gap junction expression and function with compounds, such as ATP and norepinephrine, which regulate gap junction signaling and expression. In Specific Aims 3 and 4, they will conduct similar experiments to those in Aims 1 and 2, but in whole tendon, in response to adaptive loading for up to 5 days. Connexin 43 is a mechanical load-sensitive gene. Knowledge of how tendon cells transduce and respond to mechanical load and wound signals will have impact on our understanding of how patients respond to motion therapy post-injury. Knowledge of how motion acts at the mechanistic level may lead to drug strategies for upregulating cell division and matrix expression with or without motion in aged or disabled patients.